(1) Field of the Invention
The present invention relates to an injection molded food container and method of manufacturing of the same and more particularly to an injection molded food container which is excellent in heat resistance, oil resistance and mechanical strength and is suitable for use as food containers for microwave ovens and convection ovens having a heater, and it also relates to preferable method of manufacturing the same.
(2) Description of the Related Art
Frozen foods and delicatessen type food have become very popular with recent changes of life style.
Heating devices such as microwave ovens, convection ovens having heaters and combined microwave and convection ovens are widely used for thawing or heating of frozen foods or heating of delecatessen type food owing to their convenience.
Furthermore, with changes of eating habits, it has become common to bake bread in heating devices such as convection ovens having heaters or combined microwave and convection ovens.
On the other hand, synthetic resins, for example, polyesters such as polyethylene terephthalate, polycarbonate, polyolefins such as polypropylene, polystyrene and polyvinyl chloride resin have been used for various containers.
When foods are heated by the above-mentioned heating devices, there are used containers made of, for example, polycarbonate, polypropylene, polyester, inorganic filler-containing polypropylene.
However, these conventional containers for heating foods can stand heating in microwave ovens, but have the problem that when they are heated to about 250.degree. C. by convection ovens having heaters which have become popular because of mouth-feel of the heated food or appearance such as formation of broiled marks, they undergo heat distortion and thus cannot be used for this purpose.
Therefore there is a need to distinguish between using plastic containers for microwave ovens and using containers made from the other materials for convection ovens having heaters.
Thus, these conventional plastic containers are inconvenient because they do not have sufficient heat resistance to permit their use in convection ovens having heaters.
Furthermore, even when heating is carried out by microwave oven, if the food to be enclosed or filled therein contains a specific oil, the inside surface of the container is often attacked therewith.
As combined microwave and convection ovens have become popular recently, there is much demand for a plastic container possible to be used for combined microwave and convection ovens.